Since polymers of cycloolefin monomers such as norbornene and dicyclopentadiene have low water absorptivity, low dielectric characteristics, excellent mechanical properties, and the like, application as a film in electric and electronic fields utilizing these advantages is expected.
As a method for obtaining films of the polymer of cycloolefin monomers, there are a number of reports on the approach of forming films from a non-crosslinked cycloolefin polymer which is soluble in solvents and can be molded by thermofusion.
For example, Japanese Patent Application Laid-open No. H6(1994)-298956 discloses a method of producing a linear cycloolefin polymer excelling in thermoplastic formability and forming the polymer by drawing. However, since the process requires a step of drawing the linear polymer after producing the polymer, the method is not necessarily advantageous from the viewpoint of productive efficiency.
Japanese Patent Applications Laid-open No. H5 (1993)-70655, No. H5(1993)-148413, No. H10(1998)-101907, and the like disclose a method of dissolving a linear cycloolefin polymer and casting the polymer solution. This method has an advantage of using existing film production equipment and technology, but requires a step of removing the solvent after applying the solution of linear polymer since a large amount of solvent is used. Moreover, when used as an electric insulation material, the films manufactured by this method may cause problems due to residual solvent such as copper foil peeling, blistering by gas generation, and the like.
Japanese Patent Application Laid-open No. 2001-253934 discloses a method of obtaining a crosslinked resin film by polymerizing a liquid mixture containing a metathesis polymerization catalyst and cycloolefins polymerizable by metathesis polymerization on a carrier. However, since the resulting resin film is a crosslinked resin film, adhesion strength with other materials such as a metallic foil, a substrate, and the like, sometimes is inadequate when the film is laminated with the other materials.
Japanese Patent Applications Laid-open No. 2000-327756 and No. 2001-253934 disclose a method of producing a norbornene resin film by ring-opening metathesis bulk polymerization of norbornene monomers using a ruthenium or osmium complex as a metathesis polymerization catalyst. In this method, after polymerizing the reactive solution containing the norbornene monomers and metathesis polymerization catalyst by ring-opening metathesis bulk polymerization at a prescribed temperature, the mixture is further heated to complete the polymerization and curing. However, the methods disclosed in these documents have a problem of poor production efficiency due to the requirement for controlling the heating rate to below a certain fixed rate.
WO 01/72870 discloses a method of obtaining a formed product of colorless norbornene resin by bulk polymerization of norbornene monomers containing a polymer modifier in the presence of a ruthenium catalyst. The patent specification indicates that a conventional method of bulk polymerization in the presence of a polymer modifier produces a phase-separated structure in the polymer, which results in whitened formed products and that this problem is caused by a moderate heating rate during the polymerization. The patent specification describes that a certain type of ruthenium catalyst can maintain the maximum heating rate to 20° C./sec or more due to the heat of reaction generated during the polymerization, thereby preventing whitening of the formed product.